1. Field of the Invention
The present invention relates to apparatus for producing axial tomograms which consists of an X-ray sectional view of an object.
2. Summary of the Invention
This invention relates to apparatus which can produce a cross-sectional view of an object on any photosensitive surface responsive to electro-magnetic radiation having wavelengths able to penetrate the object. The cross-sectional view is obtained after a time exposure of the photosensitive surface during which synchronized rotary motion about parallel axes is imparted to at least two of the three elements identified as follows:
A. THE RADIATION SOURCE
B. THE OBJECT WHOSE CROSS-SECTIONAL VIEW IS DESIRED
C. THE PHOTOSENSITIVE SURFACE.
Of particular interest is the case where the radiation source is an X-ray tube, the object is the skull of a living human being and the photosensitive surface is a sheet of X-ray film. Proper rotary motion of the skull and film during exposure will produce a film image, after development, representing a cross section of the skull as if it had been sliced by a plane above and parallel to the ears, permitting the upper portion to be removed and the contents to be viewed from above. For clarity here, a second analogy would be similar to sawing through the trunk of a tree so that the growth rings can be observed. Here, of course, the cross-section view is obtained by imaging X-rays without the need for physical sawing or slicing.
In current X-ray technology, the closest approach to the present invention is apparatus for generating what is alternately termed a "laminogram" or a tomogram. Such apparatus places the X-ray tube and the film on opposite sides of the object with the surface of the film facing the X-ray tube. During a time exposure, the X-ray tube and the film are simultaneously translated in parallel planes in opposite directions and at different rates.
The rates and distances are chosen so that only those features within the object which lie in one plane are imaged sharply on the film. All features above or below this plane are "blurred" during the exposure.
In short, the film which is able to integrate with respect to time and to space has performed the computer function known as "autocorrelation" in the process of producing the tomogram. The traditional tomogram, produced by the apparatus just described, produces that view which we see as the grain in a length of lumber after a tree emerges from the sawmill. By contrast, the present invention produces a view which is observed by inspecting the end of the same piece of lumber. Consistent with prior nomenclature, the end view or cross-section view obtained by X-rays will be called an "axial tomogram." Prior art devices are available which produce "computerized axial tomograms," using X-rays on human beings. The known prior art systems operate on the same basic principle in producing an axial tomogram of the brain and can be briefly described as follows.
A pencil beam of X-rays is formed by an X-ray source and a photoelectric detector situated on opposite sides of the skull which is held stationary during a five minute time exposure. During exposure the source and detector scan in synchronism along parallel paths in a straight line translating motion. After each such pass the source and detector are repositioned so that the pencil beam is rotated approximately through an angle of one degree relative to the backbone of the patient, after which the linear motion of the source and detector are reversed to make another pass. This procedure is repeated so that the combination of rotation and translation makes about 180 passes to produce a total rotation of 180.degree.. The total scanning time requires about five minutes due to the large masses being moved in a reciprocating and angularly stepped motion. During exposure, the photoelectric detector continually sends signals to a digital computer which samples the electrical signal about 180 times during each pass and converts the signal to a digital number which is stored on a magnetic disc. Upon recall, the computer generates a picture on a cathode ray tube composed of a checkerboard matrix of picture elements on the order of 180 .times. 180 for a total of 32,000 elements. The resolution of commercial television which produces a 525 .times. 525 image for a total of 275,000 picutre elements is 8.6 times as good. By the same criteria, X-ray film can produce an image composed of at least ten million picture elements which is about 300 times that produced by (C.A.T.) computerized axial tomography. Moreover, both devices described above are extremely expensive.
One objective of the present invention is to produce an axial tomogram on film having the following comparative specifications:
______________________________________ Apparatus C. A. T. Invention Scan Time 5 minutes 10 seconds Picture Elements 32,000 10,000,000 Price 10 .times. .times. Patient Position Prone Seated Total Scan Angle 180.degree. 360.degree. Scan Pattern Reciprocating Pure Rotary plus Rotary Information Flow Digital Continuous ______________________________________
Although the subsequent description of the present invention is confined, for the sake of clarity, to apparatus for producing axial tomograms of the human brain by means of X-rays, it should be emphasized that other parts of the body can be imaged by similar apparatus. It should be further emphasized that inanimate objects can be likewise imaged by X-rays or any other form of radiation which can penetrate the object and also produce a physical change on a detecting surface.
The radiating wavelengths include microwave frequencies, infra-red, visible light, ultraviolet, high energy electrons, X-rays and gamma rays all of which can be made to emanate from a point source. The choice of wavelengths will depend on the material of which the object is made. The detector surface may include film which is exposed directly by the radiation, a fluorescent surface which indirectly exposes film by either contact or projection, an image converter which responds to the radiation and through electron emission produces an image on a fluorescent screen, a surface which is electrically charged and then locally discharged by the radiation to form a charge pattern.
The primary object of the invention is to provide a low cost high speed apparatus for producing tomograms.